(1) Field of the Invention
This invention relates to a camera having a built-in battery-powered electronic strobe flash unit. More particularly, this invention provides for charging of the flash unit while a photographer is framing a scene to be photographed within the camera's viewfinder. This prevents energy from being drawn from the battery unnecessarily and permits charging of the flash unit without delaying the photographic exposure.
(2) Description of the Prior Art
A battery-powered electronic strobe flash unit draws a relatively large amount of energy from the battery for charging a capacitor to a voltage level that is necessary to fire the strobe unit's flashtube. When a flash unit is provided with a camera, an even heavier load is placed on the battery if it is also required to supply energy to other camera components such as a film transport motor. To prevent battery energy from being wasted it is desirable to charge the flash unit only if a flash exposure is to be made.
It is known in the prior art to provide for the charging of an electronic strobe flash unit in response to pre-exposure movement of a camera shutter release member so that the flash unit is charged only for a flash exposure. For example, U.S. Pat. No. 3,651,372 describes structure for charging a flash unit in response to pre-exposure movement of a release member of the illumination reflected from a scene to be photographed as below a predetermined level. A lamp is energized during flash unit charging. A camera operator is supposed to delay further actuation of the release member to open the shutter until the lamp is de-energized.
U.S. Pat. No. 3,953,864 describes apparatus for charging a flash unit in response to movement of a camera body release member when the subject brightness is below a predetermined level and the subject is within a given distance of the camera.
U.S. Pat. No. 4,007,469 describes an arrangement for charging a flash unit in response to pre-exposure movement of a camera release member if the subject brightness is below a given level. While flash charging occurs, a camera shutter is retained in a closed position.
U.S. Pat. No. 4,084,167 describes camera structure for charging a built-in strobe flash unit when a shutter release member is actuated if the scene brightness is low. An energized electromagnet latches the release member in a pre-exposure position while the flash unit charges. Once the flash is charged, the electromagnet is de-energized to unlatch the release member so that the shutter can be opened.
In the aforementioned prior art, the charging of the flash unit normally would occur only after the camera operator has framed the scene to be photographed within the camera's viewfinder. Accordingly, flash unit charging causes a delay in making an exposure, beyond the time used to aim the camera. This delay can cause loss of picture-taking opportunities, particularly those involving fast-action scenes. Furthermore, it can be annoying to a subject posing for a picture because a longer posing time is required and the additional uncertainty as to when an exposure is to occur makes it more difficult to maintain the proper pose.